Processing impedance signals for breath detection

ABSTRACT

An apparatus for assisting in providing patient ventilations includes electrodes configured to provide airflow activities signals, chest compression sensors configured to provide chest displacement signals due to chest compressions, a processor and a memory configured to receive the airflow activities and chest displacement signals, identify a presence of chest compressions based on the chest displacement signals, subsequently confirm an absence of chest compressions applied to the patient based on the chest displacement signals, adjust signal processing parameters for the airflow activities signals in response to the confirmed absence of chest compressions, and process the airflow activities signals using the adjusted signal processing parameters to determine feedback for providing the patient ventilations in the absence of chest compressions, and an output device coupled to the processor and the memory and configured to provide the ventilation feedback.

CLAIM OF PRIORITY

This application is a continuation under 35 U.S.C. § 120 of U.S. patentapplication Ser. No. 15/910,038, filed on Mar. 2, 2018, which is acontinuation of U.S. patent application Ser. No. 14/200,571, filed onMar. 7, 2014 and issued as U.S. Pat. No. 9,968,267, which claimspriority under 35 USC § 119(e) to U.S. Patent Application Ser. No.61/791,150, filed on Mar. 15, 2013. All subject matter set forth in theabove referenced applications is hereby incorporated by reference in itsentirety into the present application as if fully set forth herein.

TECHNICAL FIELD

This document relates to processing signals from a patient's chest forbreath detection, and in particular to systems and techniques forprocessing signals to monitor ventilation of the patient duringcardio-pulmonary resuscitation (CPR) treatment.

BACKGROUND

Sudden cardiac arrest (colloquially “heart attack”) is a frequent causeof death. One treatment for cardiac arrest is quick and competent chestcompressions to keep blood flowing through a patient's heart. Along withchest compressions, a rescuer may ventilate the patient by eitherexhaling into the patient's mouth or nose or utilizing a device thatpushes air into the patient's lungs. Rescuers, in particular untrainedrescuers, may experience a rush of excitement during such medicalemergencies that can result in over-ventilating the patient. Suchuntrained rescuers may consider such additional ventilations as beinghelpful to the patient; however, studies have shown the opposite.Additional cycles of inflating and deflating the patient's lungs mayraise pressure in the patient's chest causing circulation of thepatient's blood to actually decrease. As a result, the ability tomonitor ventilations and provide CPR in a competent manner can be a veryimportant personal skill, and is particularly important for professionalhealthcare workers such as emergency medical technicians (EMTs).

SUMMARY

This document describes systems and techniques for processing signalsrepresentative of airflow activities (e.g., ventilation, respiration,etc.) of a patient during CPR treatment. By accounting for signalartifacts that represent the motion of chest compressions applied duringCPR, a processed signal may be produced that more accurately representsthe airflow activities of the patient, in particular identifying theoccurrences of ventilations. Based on this information, feedback can beprovided to the rescuer, for example, to appropriately adjust the CPRtreatment being applied to the patient such as reducing ventilationfrequency so not to overly hinder blood circulation.

In one aspect, an apparatus includes a computing device that includes amemory configured to store instructions. The computing device alsoincludes a processor to execute the instructions to perform operationsthat include receiving a signal representative of electrical impedancein a chest of a patient, and, receiving a signal representative of themotion of chest compressions performed on the patient during acardiopulmonary resuscitation (CPR) treatment. The operations alsoinclude processing the received signal representative of the motion ofchest compressions to determine one or more characteristics of themotion, and, processing the received signal representative of theelectrical impedance to determine parameters relevant to a production ofa signal representative of airflow activities of the patient. Operationsalso include modifying the one or more determined parameters based onthe one or more determined characteristics of the motion to produce thesignal representative of airflow activities of the patient.

Implementations may include one or more of the following features. Thecomputing device may be capable of providing a feedback signalreflective of the airflow activities for adjusting the CPR treatment ofthe patient. The one or more determined parameters may include filteringparameters for processing the received signal representative of theelectrical impedance. The one or more determined parameters may includeone or more thresholds for processing the received signal representativeof the electrical impedance. The determined one or more characteristicsof the received signal representative of the motion of chestcompressions may reflect an absence of chest compressions beingperformed on the patient over a period of time. The determined one ormore characteristics of the received signal representative of the motionof chest compressions may represent the timing of chest compressionoccurrences. Modifying the one or more parameters may be performed inmultiple instances for adjusting the processing of the received signalrepresentative of the electrical impedance to reflect changes in thechest compressions. The signal representative of electrical impedance inthe chest of the patient may be provided by a plurality of defibrillatorelectrode pads. The signal representative of the motion of the chestcompressions may be provided by an accelerometer positioned to move incoordination with the motion of the patient's chest. The signalrepresentative of the motion of the chest compressions may be anelectrocardiogram signal from the patient.

In another aspect, one or more computer readable media storinginstructions that are executable by a processing device, and upon suchexecution cause the processing device to perform operations includingreceiving a signal representative of electrical impedance in a chest ofa patient, and, receiving a signal representative of the motion of chestcompressions performed on the patient during a cardiopulmonaryresuscitation (CPR) treatment. Operations also include processing thereceived signal representative of the motion of chest compressions todetermine one or more characteristics of the motion, and, processing thereceived signal representative of the electrical impedance to determineparameters relevant to a production of a signal representative ofairflow activities of the patient. Operations also include modifying theone or more determined parameters based on the one or more determinedcharacteristics of the motion to produce the signal representative ofairflow activities of the patient.

Implementations may include one or more of the following features. Thecomputing device may be capable of providing a feedback signalreflective of the airflow activities for adjusting the CPR treatment ofthe patient. The one or more determined parameters may include filteringparameters for processing the received signal representative of theelectrical impedance. The one or more determined parameters may includeone or more thresholds for processing the received signal representativeof the electrical impedance. The determined one or more characteristicsof the received signal representative of the motion of chestcompressions may reflect an absence of chest compressions beingperformed on the patient over a period of time. The determined one ormore characteristics of the received signal representative of the motionof chest compressions may represent the timing of chest compressionoccurrences. Modifying the one or more parameters may be performed inmultiple instances for adjusting the processing of the received signalrepresentative of the electrical impedance to reflect changes in thechest compressions. The signal representative of electrical impedance inthe chest of the patient may be provided by a plurality of defibrillatorelectrode pads. The signal representative of the motion of the chestcompressions may be provided by an accelerometer positioned to move incoordination with the motion of the patient's chest. The signalrepresentative of the motion of the chest compressions may be anelectrocardiogram signal from the patient.

In another aspect, a computing device implemented method includesreceiving a signal representative of electrical impedance in a chest ofa patient, and, receiving a signal representative of the motion of chestcompressions performed on the patient during a cardiopulmonaryresuscitation (CPR) treatment. The method also includes processing thereceived signal representative of the motion of chest compressions todetermine one or more characteristics of the motion, and, processing thereceived signal representative of the electrical impedance to determineparameters relevant to a production of a signal representative ofairflow activities of the patient. The method also includes modifyingthe one or more determined parameters based on the one or moredetermined characteristics of the motion to produce the signalrepresentative of airflow activities of the patient.

Implementations may include one or more of the following features. Thecomputing device may be capable of providing a feedback signalreflective of the airflow activities for adjusting the CPR treatment ofthe patient. The one or more determined parameters may include filteringparameters for processing the received signal representative of theelectrical impedance. The one or more determined parameters may includeone or more thresholds for processing the received signal representativeof the electrical impedance. The determined one or more characteristicsof the received signal representative of the motion of chestcompressions may reflect an absence of chest compressions beingperformed on the patient over a period of time. The determined one ormore characteristics of the received signal representative of the motionof chest compressions may represent the timing of chest compressionoccurrences. Modifying the one or more parameters may be performed inmultiple instances for adjusting the processing of the received signalrepresentative of the electrical impedance to reflect changes in thechest compressions. The signal representative of electrical impedance inthe chest of the patient may be provided by a plurality of defibrillatorelectrode pads. The signal representative of the motion of the chestcompressions may be provided by an accelerometer positioned to move incoordination with the motion of the patient's chest. The signalrepresentative of the motion of the chest compressions may be anelectrocardiogram signal from the patient.

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features and advantages willbe apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a caregiver using a system for responding to anemergency medical condition.

FIG. 2 illustrates signals used for detecting airflow activities of apatient.

FIG. 3 is a flow chart of operations for processing signals fordetecting airflow activities.

FIGS. 4a and b illustrate the processing of signals for detecting anairflow activity of a patient.

FIG. 5 is a flow chart of operations for processing signals fordetecting airflow activities.

FIG. 6 shows an example of a generic computer device and a genericmobile computer device, which may be used with the techniques describedhere.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Referring to FIG. 1, at a rescue scene 100, a caregiver 104 performscardiopulmonary resuscitation (CPR) on a victim or patient 102 (theterms are used interchangeably here to indicate a person who is thesubject of intended or actual CPR and related treatment, or othermedical treatment), such as an individual who has apparently undergonesudden cardiac arrest. The caregiver 104 may be, for instance, acivilian responder with limited or no training in lifesaving techniques;a first responder, such as an emergency medical technician (EMT), policeofficer, or firefighter; or a medical professional, such as a physicianor nurse. The caregiver 104 may be acting alone or may be acting withassistance from one or more other caregivers, such as a partner EMT.

In this illustration, the caregiver 104 can deploy a self-containedresponse unit 106 for use with an electronic defibrillating systemincluding a defibrillator, such as an automated external defibrillator(AED) 108, a professional defibrillator, or another type ofdefibrillating apparatus. The AED 108 may take a variety of forms, suchas the ZOLL MEDICAL R Series, E Series, or X Series defibrillators. Inthis example, the response unit 106 includes an assembly of electrodepads 110 through which the AED 108 can provide defibrillation to thepatient 102. The response unit 106 also includes one or more sensorsthat provide signals to the AED 108, based on which the AED 108 caninstruct the caregiver 104 in performing CPR. For example, theelectrical impedance present in the chest of the patient 102 may bemeasured between the electrode pads of the assembly 110 and provided ina signal to the AED 108. Such an impedance signal may be used for avariety of operations of the AED 108, for example, based upon themeasured impedance, the AED 108 may adjust the amount of current appliedto the victim's heart during defibrillation (e.g., high impedance maycall for an increased current level). The impedance across the patient'schest can also be used to detect the airflow activities (e.g.,respiration, ventilation, etc.) of the victim. As the patient's lungsexpand and contract, the geometry of the patient's chest changes thatcauses the measured impedance to correspondingly change.

The electrode pad assembly 110 may also include one or more sensors forcollecting other signals and sensing other phenomena. For example, theelectrode pad assembly 110 may include one or more sensors forcollecting electrocardiogram (ECG) signals read from the patient 102.The assembly of electrode pads 110 may also include one or more sensorsmeasuring chest compressions applied to the patient 102. For example, asensor may be positioned in a location where the caregiver 104 is toplace the palms of their hands when performing CPR chest compressions onthe patient. As a result, the sensor may move with the victim's chestand the caregiver's hands, and provide a measure of the verticaldisplacement of such motion.

In this example, the self-contained response unit 106 also includes aventilation bag 112, shown sealed around the mouth of the victim 102.The ventilation bag 112 may, for the most part, takes a familiar form,and may include a flexible body structure that the caregiver 104 maysqueeze periodically to provide ventilation on the patient 102 when thepatient is not breathing sufficiently on his or her own.

As mentioned above, over ventilating the patient 102 (e.g., due to anoverly-excited novice caregiver), may cause a variety of repercussions.For example, inflating the victim's lungs too frequently may result inexcess pressure being placed on the victim's heart that can prevent anaccurate supply of blood from being provided to the heart and circulatedthroughout the patient's body. As such, monitoring the ventilationsbeing applied to the victim and providing the caregiver 104 feedbackregarding the ventilations (e.g., inform the caregiver to reduce thefrequency of ventilations, etc.) may be crucial for the patient's bloodcirculation.

Referring to FIG. 2, one or more techniques may be implemented forattaining a measure of the ventilations being applied to the patient 102or other types of airflow activities associated with the patient (e.g.,unassisted inhaling and exhaling of the patient, etc.). For example, animpedance signal measured across the chest of the patient 102 may beprocessed for representing airflow activities (e.g., ventilations,unassisted breathing by the patient, etc.) and to determine if thepatient is being over ventilated. As illustrated in the figure, arepresentation of the upper portion of the victim 102 is illustrated topresent the deployed assembly of electrode pads 110. Two signals areillustrated as being provided to the AED 108 from the assembly ofelectrode pads 110. In particular, an impedance signal (graphicallyrepresented by arrow 200) is provided to the AED 108. In this particulararrangement, the impedance signal is provided by passing electricalcurrent between two electrodes 202, 204, however, other techniques maybe employed for measuring electrical impedance across the patient'schest. Also, different types of electrode configurations may beimplemented. For example, more than two electrodes may be used in somearrangements for measuring the impedance present in the patient's chest.

In general, the level of impedance represented by the impedance signal200 varies as the geometry of patient's chest changes due to the volumeof air introduced by the ventilation bag 112 (shown in FIG. 1). Bydetecting the corresponding change in the impedance signal, asubstantially accurate count of the ventilations may be determined alongwith other associated characteristics (e.g., ventilation rate, etc.).However, often other activities associated with the CPR treatment beingapplied to the victim may influence or even corrupt the impedance signaland thereby affect the accuracy of the ventilation count determined bythe AED 108. For example, chest compressions performed by the caregiver104 may also cause a change in the geometry of the patient's chest andcorresponding cause electrical impedance fluctuations. Since changes inthe impedance signal may also reflect chest compressions, the signal maynot provide an accurate measure of the ventilations applied to thepatient 102 and the AED may incorrectly determine that the patient isbeing over ventilated, or possibly worse, that the patient is beingproperly ventilated when in actuality the patient is being overventilated.

One or more techniques and methodologies may be implemented to addressthe potentially corrupting influences on the impedance signal by thechest compressions applied by the caregiver 104. For example, theimpedance signal provided by the assembly of electrode pads 110 may beprocessed to account for the applied chest compressions. In thisparticular example, a signal (graphically represented by the arrow 206)is provided to the AED 108 that represents the applied chestcompressions. By using this chest compression signal, the AED 108 mayprocess the impedance signal to substantially remove artifacts includedin the impedance signal that represent the chest compressions andthereby provide a more accurate count of the ventilations applied to thepatient 102.

One or more techniques may be implemented for producing a signalrepresentative of chest compressions applied to a patient. For example,the assembly of electrode pads 110 may also include a center portion atwhich an accelerometer assembly 208 is mounted. The accelerometerassembly 208 may include a housing inside which is mounted anaccelerometer sensor configuration. The accelerometer assembly 208 maybe positioned in a location where the caregiver 104 is to place thepalms of their hands when performing CPR chest compressions on thepatient 102. As a result, the accelerometer assembly 208 may move withthe patient's 102 chest and the caregiver's hands, and acceleration ofsuch movement may be double-integrated to identify a verticaldisplacement of such motion. In some arrangements the accelerometerassembly 208 may include two or more accelerometer that may be used inconcert to provide the chest compression signal (e.g., provide anaveraged signal from the multiple sensors) to the AED 108. Further,other types of technology may be employed alone or in combination (e.g.,in concert with the accelerometer assembly 208) to produce a signalrepresentative of chest compressions. For example, one or more pressuresensors, ultrasound technology, string gauges, laser interferometry,magnetic field technology, cameras, etc. may be implemented forproviding chest compression signals. Different types of signals may alsobe used for attaining information representative of chest compressions.For example, one or more ECG signals collected from a patient (e.g., bythe electrode pad assembly 110) may be used for identifying chestcompression during CPR treatment. In some arrangements, the impedancesignal (or another impedance signal may be used for identifying chestcompressions).

Provided the impedance signal 200 and the chest compression signal 206,the AED 108 may implement one or more techniques to process the signalsto identify airflow activities of the patient 102 such as occurrences ofventilations, unassisted respiratory activities, etc. As illustrated inthe figure, the AED 108 includes a signal processor 210 that processesthe provided signals. The signal processor 210 may be software based(e.g., one or more processes, routines, operations, functions, etc.),hardware based (e.g., one or more general processing units, specializedprocessing units, etc.), implemented in software and hardware, etc. Inaddition to using the information provided by the signals (e.g., theimpedance signal, chest compression signal, etc.), the signal processor210 may also use information from other sources, for example, locallystored data (e.g., stored in one or more memories in the AED 108), datastored external to the AED (e.g., in one or more remote memories thatmay or may not be network accessible), etc. By processing the receivedsignals, and potentially using other information, the signal processor210 may initiate the production of one or more signals for alerting thecaregiver 104. For example, one or more feedback signals (e.g., anaudible alert signal 212) may be produced and provided to the caregiver104 for initiating appropriate action (e.g., reduce the frequency ofventilations applied to the patient). Other types of feedback signalsmay also be initiated by the signal processor 210. For example, visualsignals provided from a series of light emitting diodes (LEDs), one ormore graphical displays, etc. may be used for providing feedback (e.g.,alerts, instructions, etc.) to the caregiver 104.

One or more techniques may be implemented by the signal processor 210 toproduce a signal that represents ventilations of the patient 102 orother types of airflow activities associated with the patient. Forexample, the chest compression signal 206 may be used to determine oneor more characteristics associated with the chest motion (e.g.,compression depth, timing, rate, etc.). The impedance signal may be usedto determine one or more parameters (e.g., filtering parameters,thresholds, etc.) relevant for producing a signal representative ofairflow activities of the patient. Once determined, parameters may bemodified (e.g., cutoff frequency changed, thresholds increased ordecreased, etc.) for processing the impedance signal 200 tosubstantially remove artifacts present in the impedance signal thatcorrespond to the performed chest compressions. By removing theartifacts due to the chest compressions, the processed impedance signalmay be more representative of airflow activities such as ventilationsand less likely of representing geometry changes of the victim's chestdue to applied compressions. For one potential processing technique,particular parameters may be identified by the signal processor 210 fromthe chest compression signal 206. For example, one or more filteringparameters (e.g., filter coefficients, cut off frequencies, etc.) may beidentified from the chest compression signal, appropriately modified,and used to filter the impedance signal. Other parameters may also beidentified, for example, one or more threshold values may be identifiedand used to define the occurrence of individual ventilations (or othertypes of airflow activities) from the impedance signal 200. In someimplementations parameters may be determined for other types of airflowactivities.

In addition to determining and using such parameters for processing theimpedance signal, the parameters may be adjusted over time. For example,filtering and threshold parameters may be adjusted based upon changes inchest compressions being applied to the victim. As such, the processingof the impedance signal may be considered adaptive to changes in theapplied chest compressions. Parameters may also be determined based uponno chest compressions being detected. For example, if determined that nocompressions are being applied (e.g., from the chest compression signal206) over a period of time (e.g., a few seconds), parameters forprocessing the impedance signal may be changed (e.g., change filtercoefficients, threshold levels, etc.). With compressions absent, theimpedance signal can be considered less corrupted and processing toaccount for compressions can be downplayed. Once compressions reappear(or newly appear) and are detected, the parameters may be adjusted againto account for the influences of the compressions in the impedancesignal.

Referring to FIG. 3, a flowchart 300 is presented that representsoperations of signal processor 210 (shown in FIG. 2) for processing animpedance signal (e.g., such as impedance signal 200 as provided from apair of defibrillator electrodes). Once received, the impedance signalmay be scaled 302. For example, the impedance values may be scaled byone or more quantities (e.g., using the least significant bit of thediscrete values) convert the signal from digital units to physical units(e.g., milli-Ohm) in preparation of the following processing operations.Once scaled, the impedance signal may be processed to substantiallyremove 304 any constant offset. For example, a smoothed version of theimpedance signal (e.g., a low pass filtered version of the impedancesignal) may be subtracted from the originally scaled impedance signal.Along with removing offset, such processing generally removes the lowfrequency baseline wander from the impedance signal.

After processing the impedance signal for offset removal, the signal isfiltered 306 to focus subsequent processing on the spectral portion ofthe signal that represents airflow activities such as ventilating apatient. One or more techniques or methodologies may be implemented forfiltering the impedance signal to produce a signal that retains thisspectral portion while removing energy of the spectrum external to theportion of interest. For example, by applying low pass and high passfilters to the impedance signal, the spectral portion of interest may besubstantially isolated for further processing by the signal processor.Further, by using information (e.g., motion characteristics) provided bythe chest compression signal, parameters for one or more of the filtersmay be defined and modified such that energy associated with the chestcompressions is removed from the impedance signal. In one filteringarrangement, first a low pass filter is applied to the impedance signal.In general, the frequency of chest compression is larger than thefrequency of ventilation cycles (or other types of airflow activities).As such, the spectral content from the chest compressions may besignificantly reduced by applying a low pass filter with a cutofffrequency located below the chest compression spectral region of thesignal (and located above the spectral region of the ventilations). Forexample, the chest compression signal may provide a compression rate of80 to 120 compressions per minute which correspond to a frequency rangeof 1.33 Hz to 2.0 Hz. Airflow activities such as ventilations occur atapproximately 6 to 10 instances per minute, which corresponds to afrequency range of 0.1 Hz to 0.166 Hz. Based on the chest compressionsignal, a cutoff frequency (e.g., to 0.5 Hz) for the low pass filter maybe set such that spectral content of ventilations fall into the passband of the filter while spectral content due to the chest compressionsmay be substantially removed from the signal. Various types of filtersand filtering techniques (e.g., single stage, multi-stage filters) maybe used to implement the low pass filter. For example, a 4th-orderButterworth filter may be implemented to provide a low pass filter forprocessing the impedance signal.

After applying a low pass filter to substantially remove the spectralcontent of the chest compression signal, the processed impedance signalmay be further filtered to isolate the spectral content of theventilations (or other type of airflow activity of the patient). Forexample, a high pass filter may be applied for removing spectral contentof the signal located at frequencies below the spectral region of theventilations. In one implementation, the high pass filter may beachieved in a two-step operation by first low pass filtering theimpedance signal and then subtracting the resulting signal from theimpedance signal. In other words, first identifying the low frequencyspectral content to be removed from the impedance signal (i.e., by lowpass filtering the signal), and second subtracting this identified lowfrequency spectral content from the impedance signal. By applying such ahigh pass filter after applying a low pass filter, the spectral regionof interest (associated with the ventilations) can be consideredisolated for additional processing (e.g., defining individualventilations applied to the victim, determining a ventilation rate,etc.).

After filtering the impedance signal, the signal processor may define308 a detection function from the filtered signal. In general, since thefiltered impedance signal may still have noisy artifacts, thresholdvalues can be defined to assist in identifying individual ventilationcycles (e.g., lungs inflating to initiate a ventilation cycle, lungsdeflating at the end of the cycle, etc.) or other types of airflowactivity events. Similar to selecting filtering parameters, thresholdvalues may depend upon information (e.g., motion characteristics)determined from the chest compression signal 206 (shown in FIG. 2). Forexample, one set of thresholds may be used if chest compressions arerepresented in chest compression signal while another set of thresholdsmay be used if there appears to be no chest compressions being appliedto the patient (as represented by the chest compression signal).

Referring to FIG. 4a , three signals are presented for demonstrating onetechnique of defining and using thresholds to identify a ventilationcycle (or other type of airflow activity). In the illustration, anarrowed line 400 represents increasing time for the viewer's left toright. For ease of viewing, a portion of a filtered impedance signal 402is presented that generally increases with positive amplitude and thendecreases into negative amplitude values with the passage of time.

One or more techniques may be implemented for defining thresholds toidentify ventilations. For example, first a baseline threshold signalmay be calculated by further filtering the filtered impedance signal402. In one arrangement, a finite impulse response (FIR) filter mayapply a low pass filter (e.g., with a cutoff frequency of 0.3 Hz) to thefiltered impedance signal to produce baseline threshold signal. In someimplementations, operations may be executed (e.g., by the signalprocessor 210) to take corrective action due to using an FIR filter. Forexample, an FIR filter may induce a phase shift in the signal beingfiltered. By storing the signal in a buffer (or other type of memorystore), retrieval of the signal (e.g., by the signal processor 210) maybe delayed from the buffer to induce a corrective phase shift.

Once the baseline threshold signal is produced, positive and negativethreshold signals may be produced for application to the filteredimpedance signal 402. One or more techniques may be implemented fordefining such signals. For example, a constant value such as the maximumvalue of the filtered impedance signal over a period of time (e.g., thecurrent portion of the filtered impedance signal and the previous fiveseconds of the filtered impedance signal) may be added to the baselinethreshold signal. Next, the values of the resulting signal may bedivided by a constant value (e.g., a value of two) to produce a positivethreshold signal 404. Similarly, a negative threshold signal 406 may beproduced by identifying a constant value such as the minimum value(i.e., a negative value) of the filtered impedance signal over a periodof time (e.g., the same time period used to produce the positivethreshold signal) and added to the baseline threshold signal. Alsosimilar to the positive threshold signal, the resulting signal may bedivided by a constant (e.g., the same value of two) to produce thenegative threshold signal 406.

With the positive and negative threshold signals 404, 406 produced,ventilations may be identified from the filtered impedance signal 402.For example a ventilation may be identified from instances when thefiltered impedance signal exceeds the positive threshold signal. In thisexample, points 408 and 410 identify such locations in which thefiltered impedance signal 402 exceeds the positive threshold signal 404.In a similar manner, points 412 and 414 identify locations in which thefiltered impedance signal 402 has drops below the negative values of thenegative threshold signal 406. Referring to FIG. 4b , from the detectedpoints 408, 410, 412, 414 a corresponding detection function 416 isproduced (e.g., by the signal processor 210) in which a constant value(e.g., +1) is assigned to time instances when the filtered impedancesignal exceeded the positive threshold signal 404, and, a differentconstant value (e.g., −1) is assigned to time instances when thefiltered impedance signal falls below the negative threshold signal 406.For time instances when the filtered impedance signal falls between thethreshold signals, another constant value is assigned (e.g., a value of0).

Returning to the flowchart 300 presented in FIG. 3, after defining thedetection function, the signal processor 210 may determine 310 if aventilation (or other type of airflow activity) has occurred. One ormore techniques may be implemented for such determinations, for example,one or more rules may be used in concert with the detection function.For example, one rule for defining a ventilation may call for thedetection function to have a value of “+1”, followed by a value of “0”,followed by a value of “−1”, followed by a value “0”. If such a sequenceof values is identified, the signal processor 210 may determine that aventilation has occurred. Time based rules may also factor intodetermining if a ventilation has occurred. For example, if the sequenceof values (e.g., “+1” follow by “0” “−1” and another “0”) occurs over aperiod of time that is less than a predefined amount (e.g., 0.9 second)or greater than another predefined amount (e.g., 20 seconds), thesequence is typically considered a non-detection (e.g., noise). Othertypes of rules may also be defined for determining if an airflowactivity has occurred. For example, rather than detecting ventilations,rules may be defined for detecting respiratory activity (e.g., thepatient inhaling and exhaling unassisted).

If determined that one or more ventilations (or other types of airflowactivities) have occurred, the signal processor 210 may calculate 312characteristics of the ventilation or ventilations. For example, thetime length of individual ventilations may be calculated. Time periodsbetween ventilations may also be determined, for example, by determiningthe time difference between the detection of two peak values present inthe detection function. If determined that a ventilation has notoccurred, or after calculating any ventilation characteristic(s), thesignal processor may present 314 results from the attained information.For example, along with presenting that one or more ventilation haveoccurred, the signal processor 210 may use this information to determineif ventilations are being appropriately applied (e.g., determine if aventilation rate threshold has been exceeded). If ventilations are beingimproperly applied, the signal processor 210 may initiate an alertsignal (e.g., the audible signal 212) indicating the caregiver'sventilation technique is flawed and may provide corrective instructions(e.g., inform the caregiver that the ventilation rate should be slowed).

Referring to FIG. 5, a flowchart 500 represents operations of a signalprocessor (e.g., the signal processor 210 shown in FIG. 2). Operationsof the signal processor are typically executed by a single computingdevice such as a defibrillator (e.g., the AED 108), a component of anelectronic defibrillating system, etc. However, the operations may alsobe executed on other types of computing devices such as other kinds ofemergency equipment. Operations of the signal processor may also beexecuted by multiple computing devices (e.g., multiple AEDs, an AED anda server, etc.). Along with being executed at a single site (e.g., thesite of a medical emergency), execution of operations may be distributedamong two or more locations (e.g., the site of the emergency and amedical facility).

Operations of the signal processor may include receiving 502 a signalrepresentative of electrical impedance in a chest of a patient. Forexample, a signal may be received from a pair of defibrillator electrodepads applied to the chest of a patient during a medical emergency.Operations may also include receiving 504 a signal representative of themotion of chest compressions performed on the patient during a CPRtreatment. For example, one or more motion sensing devices (e.g., anaccelerometer, pressure sensor, etc.) may be implemented to provide asignal representative of the compressions. Operations may also includeprocessing 506 the received signal representative of the motion of chestcompressions to determine one or more characteristics of the motion. Forexample, compression depth, time, rate, etc. may be determined from thechest compression signal. Operations may also include processing 508 thereceived signal representative of the electrical impedance to determineparameters relevant to a production of a signal representative ofairflow activities of the patient. For example, filter coefficients, cutoff frequencies, threshold values, etc. may be determined for processingthe impedance signal. Operations may also include modifying 510 the oneor more determined parameters based on the one or more determinedcharacteristics of the motion to produce the signal representative ofairflow activities of the patient. For example, after one or moreparameters (e.g., cutoff frequencies, etc.) are modified (e.g., valuesadjusted) based on the motion characteristics (e.g., compression rate,etc.), the impedance signal may be filtered one or more times (and insome implementations, in an adaptive manner) to substantially removesignal artifacts caused by the chest compressions and embedded in theimpedance signal. One or more thresholds may also be modified andapplied to impedance signal to further reduce the influencing effects ofthe chest compressions and to provide an accurate detection ofventilations applied to the patient during CPR. Once the ventilations orother type of airflow activities are detected, analysis operations maybe executed to expose improper CPR treatment techniques (e.g., excessiveventilation cycles) and possibly suggest corrective action (e.g., alertthe caregiver to slow the ventilation cycles).

FIG. 6 shows an example of example computer device 600 and examplemobile computer device 650, which can be used to implement thetechniques described herein. For example, a portion or all of theoperations of the signal processor 210 (shown in FIG. 2) for processingimpedance and chest compression signals may be executed by the computerdevice 600 and/or the mobile computer device 650. Computing device 600is intended to represent various forms of digital computers, including,e.g., laptops, desktops, workstations, personal digital assistants,servers, blade servers, mainframes, and other appropriate computers.Computing device 650 is intended to represent various forms of mobiledevices, including, e.g., personal digital assistants, tablet computingdevices, cellular telephones, smartphones, and other similar computingdevices. The components shown here, their connections and relationships,and their functions, are meant to be examples only, and are not meant tolimit implementations of the techniques described and/or claimed in thisdocument.

Computing device 600 includes processor 602, memory 604, storage device606, high-speed interface 608 connecting to memory 604 and high-speedexpansion ports 610, and low speed interface 612 connecting to low speedbus 614 and storage device 606. Each of components 602, 604, 606, 608,610, and 612, are interconnected using various busses, and can bemounted on a common motherboard or in other manners as appropriate.Processor 602 can process instructions for execution within computingdevice 600, including instructions stored in memory 604 or on storagedevice 606 to display graphical data for a GUI on an externalinput/output device, including, e.g., display 616 coupled to high speedinterface 608. In other implementations, multiple processors and/ormultiple buses can be used, as appropriate, along with multiple memoriesand types of memory. Also, multiple computing devices 600 can beconnected, with each device providing portions of the necessaryoperations (e.g., as a server bank, a group of blade servers, or amulti-processor system).

Memory 604 stores data within computing device 600. In oneimplementation, memory 604 is a volatile memory unit or units. Inanother implementation, memory 604 is a non-volatile memory unit orunits. Memory 604 also can be another form of computer-readable medium,including, e.g., a magnetic or optical disk. Memory 604 may benon-transitory.

Storage device 606 is capable of providing mass storage for computingdevice 600. In one implementation, storage device 606 can be or containa computer-readable medium, including, e.g., a floppy disk device, ahard disk device, an optical disk device, or a tape device, a flashmemory or other similar solid state memory device, or an array ofdevices, including devices in a storage area network or otherconfigurations. A computer program product can be tangibly embodied in adata carrier. The computer program product also can contain instructionsthat, when executed, perform one or more methods, including, e.g., thosedescribed above. The data carrier is a computer- or machine-readablemedium, including, e.g., memory 604, storage device 606, memory onprocessor 602, and the like.

High-speed controller 608 manages bandwidth-intensive operations forcomputing device 600, while low speed controller 612 manages lowerbandwidth-intensive operations. Such allocation of functions is anexample only. In one implementation, high-speed controller 608 iscoupled to memory 604, display 616 (e.g., through a graphics processoror accelerator), and to high-speed expansion ports 610, which can acceptvarious expansion cards (not shown). In the implementation, low-speedcontroller 612 is coupled to storage device 606 and low-speed expansionport 614. The low-speed expansion port, which can include variouscommunication ports (e.g., USB, Bluetooth®, Ethernet, wirelessEthernet), can be coupled to one or more input/output devices,including, e.g., a keyboard, a pointing device, a scanner, or anetworking device including, e.g., a switch or router, e.g., through anetwork adapter.

Computing device 600 can be implemented in a number of different forms,as shown in the figure. For example, it can be implemented as standardserver 620, or multiple times in a group of such servers. It also can beimplemented as part of rack server system 624. In addition or as analternative, it can be implemented in a personal computer including,e.g., laptop computer 622. In some examples, components from computingdevice 600 can be combined with other components in a mobile device (notshown), including, e.g., device 650. Each of such devices can containone or more of computing device 600, 650, and an entire system can bemade up of multiple computing devices 600, 650 communicating with eachother.

Computing device 650 includes processor 652, memory 664, an input/outputdevice including, e.g., display 654, communication interface 666, andtransceiver 668, among other components. Device 650 also can be providedwith a storage device, including, e.g., a microdrive or other device, toprovide additional storage. Each of components 650, 652, 664, 654, 666,and 668, are interconnected using various buses, and several of thecomponents can be mounted on a common motherboard or in other manners asappropriate.

Processor 652 can execute instructions within computing device 650,including instructions stored in memory 664. The processor can beimplemented as a chipset of chips that include separate and multipleanalog and digital processors. The processor can provide, for example,for coordination of the other components of device 650, including, e.g.,control of user interfaces, applications run by device 650, and wirelesscommunication by device 650.

Processor 652 can communicate with a user through control interface 658and display interface 656 coupled to display 654. Display 654 can be,for example, a TFT LCD (Thin-Film-Transistor Liquid Crystal Display) oran OLED (Organic Light Emitting Diode) display, or other appropriatedisplay technology. Display interface 656 can comprise appropriatecircuitry for driving display 654 to present graphical and other data toa user. Control interface 658 can receive commands from a user andconvert them for submission to processor 652. In addition, externalinterface 662 can communicate with processor 652, so as to enable neararea communication of device 650 with other devices. External interface662 can provide, for example, for wired communication in someimplementations, or for wireless communication in other implementations,and multiple interfaces also can be used.

Memory 664 stores data within computing device 650. Memory 664 can beimplemented as one or more of a computer-readable medium or media, avolatile memory unit or units, or a non-volatile memory unit or units.Expansion memory 674 also can be provided and connected to device 650through expansion interface 672, which can include, for example, a SIMM(Single In Line Memory Module) card interface. Such expansion memory 674can provide extra storage space for device 650, or also can storeapplications or other data for device 650. Specifically, expansionmemory 674 can include instructions to carry out or supplement theprocesses described above, and can include secure data also. Thus, forexample, expansion memory 674 can be provided as a security module fordevice 650, and can be programmed with instructions that permit secureuse of device 650. In addition, secure applications can be providedthrough the SIMM cards, along with additional data, including, e.g.,placing identifying data on the SIMM card in a non-hackable manner.

The memory can include, for example, flash memory and/or NVRAM memory,as discussed below. In one implementation, a computer program product istangibly embodied in a data carrier. The computer program productcontains instructions that, when executed, perform one or more methods,including, e.g., those described above. The data carrier is a computer-or machine-readable medium, including, e.g., memory 664, expansionmemory 674, and/or memory on processor 652, which can be received, forexample, over transceiver 668 or external interface 662.

Device 650 can communicate wirelessly through communication interface666, which can include digital signal processing circuitry wherenecessary. Communication interface 666 can provide for communicationsunder various modes or protocols, including, e.g., GSM voice calls, SMS,EMS, or MMS messaging, CDMA, TDMA, PDC, WCDMA, CDMA2000, or GPRS, amongothers. Such communication can occur, for example, throughradio-frequency transceiver 668. In addition, short-range communicationcan occur, including, e.g., using a Bluetooth®, WiFi, or other suchtransceiver (not shown). In addition, GPS (Global Positioning System)receiver module 670 can provide additional navigation- andlocation-related wireless data to device 650, which can be used asappropriate by applications running on device 650. Sensors and modulessuch as cameras, microphones, compasses, accelerators (for orientationsensing), etc. maybe included in the device.

Device 650 also can communicate audibly using audio codec 660, which canreceive spoken data from a user and convert it to usable digital data.Audio codec 660 can likewise generate audible sound for a user,including, e.g., through a speaker, e.g., in a handset of device 650.Such sound can include sound from voice telephone calls, can includerecorded sound (e.g., voice messages, music files, and the like) andalso can include sound generated by applications operating on device650.

Computing device 650 can be implemented in a number of different forms,as shown in the figure. For example, it can be implemented as cellulartelephone 680. It also can be implemented as part of smartphone 682,personal digital assistant, or other similar mobile device.

Various implementations of the systems and techniques described here canbe realized in digital electronic circuitry, integrated circuitry,specially designed ASICs (application specific integrated circuits),computer hardware, firmware, software, and/or combinations thereof.These various implementations can include implementation in one or morecomputer programs that are executable and/or interpretable on aprogrammable system including at least one programmable processor, whichcan be special or general purpose, coupled to receive data andinstructions from, and to transmit data and instructions to, a storagesystem, at least one input device, and at least one output device.

These computer programs (also known as programs, software, softwareapplications or code) include machine instructions for a programmableprocessor, and can be implemented in a high-level procedural and/orobject-oriented programming language, and/or in assembly/machinelanguage. As used herein, the terms machine-readable medium andcomputer-readable medium refer to a computer program product, apparatusand/or device (e.g., magnetic discs, optical disks, memory, ProgrammableLogic Devices (PLDs)) used to provide machine instructions and/or datato a programmable processor, including a machine-readable medium thatreceives machine instructions.

To provide for interaction with a user, the systems and techniquesdescribed here can be implemented on a computer having a display device(e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor)for displaying data to the user and a keyboard and a pointing device(e.g., a mouse or a trackball) by which the user can provide input tothe computer. Other kinds of devices can be used to provide forinteraction with a user as well; for example, feedback provided to theuser can be a form of sensory feedback (e.g., visual feedback, auditoryfeedback, or tactile feedback); and input from the user can be receivedin a form, including acoustic, speech, or tactile input.

The systems and techniques described here can be implemented in acomputing system that includes a back end component (e.g., as a dataserver), or that includes a middleware component (e.g., an applicationserver), or that includes a front end component (e.g., a client computerhaving a user interface or a Web browser through which a user caninteract with an implementation of the systems and techniques describedhere), or a combination of such back end, middleware, or front endcomponents. The components of the system can be interconnected by a formor medium of digital data communication (e.g., a communication network).Examples of communication networks include a local area network (LAN), awide area network (WAN), and the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

In some implementations, the engines described herein can be separated,combined or incorporated into a single or combined engine. The enginesdepicted in the figures are not intended to limit the systems describedhere to the software architectures shown in the figures.

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications can be made without departing fromthe spirit and scope of the processes and techniques described herein.In addition, the logic flows depicted in the figures do not require theparticular order shown, or sequential order, to achieve desirableresults. In addition, other steps can be provided, or steps can beeliminated, from the described flows, and other components can be addedto, or removed from, the described systems. Accordingly, otherembodiments are within the scope of the following claims.

What is claimed is:
 1. An apparatus for assisting ventilations providedto a patient, the apparatus comprising: a plurality of electrodesconfigured to provide signals representative of airflow activities ofthe patient; one or more chest compression sensors configured to providesignals representative of chest displacement due to chest compressions;a processor and a memory configured to: receive the signalsrepresentative of the airflow activities of the patient from theplurality of electrodes, receive the signals representative of chestdisplacement due to chest compressions from the one or more chestcompression sensors, identify a presence of chest compressions appliedto the patient based on the signals representative of chestdisplacement, subsequent to identification of the presence of chestcompressions, confirm an absence of chest compressions applied to thepatient based on the signals representative of chest displacement,adjust one or more signal processing parameters for the signalsrepresentative of the airflow activities of the patient in response tothe confirmed absence of chest compressions applied to the patient, andprocess the signals representative of the airflow activities of thepatient using the adjusted one or more signal processing parameters todetermine feedback for providing the ventilations to the patient in theabsence of chest compressions; and an output device coupled to theprocessor and the memory and configured to provide the feedback forproviding the ventilations of the patient.
 2. The apparatus of claim 1,wherein the signals representative of the airflow activities of thepatient comprise signals indicative of changes to a patient chestgeometry.
 3. The apparatus of claim 2, wherein the signalsrepresentative of airflow activities comprise electrical impedancesignals measured across the chest of the patient.
 4. The apparatus ofclaim 3, wherein the one or more signal processing parameters compriseone or more threshold values for processing the electrical impedancesignals.
 5. The apparatus of claim 4, wherein the one or more thresholdvalues comprise a first set of thresholds for use in the presence ofchest compressions applied to the patient and a second set of thresholdsfor use in the absence of chest compressions applied to the patient, andwherein the processor is configured to change the one or more signalprocessing parameters the first set of thresholds to the second set ofthresholds in response to the confirmed absence of chest compressionsapplied to the patient.
 6. The apparatus of claim 4, wherein the one ormore signal processing parameters comprise signal filters.
 7. Theapparatus of claim 1, wherein the processor is configured to: identify aperiod of time associated with the absence of chest compressions, andchange the one or more signal processing parameters when the period oftime reaches a predetermined value.
 8. The apparatus of claim 7, whereinthe predetermined value is 1-5 seconds.
 9. The apparatus of claim 1,wherein the processor is configured to: identify a resumption of chestcompressions based on the signals representative of chest displacement,and change the one or more signal processing parameters in response tothe identified resumption of chest compressions.
 10. The apparatus ofclaim 1, wherein the plurality of electrodes comprise ECG electrodes.11. The apparatus of claim 1, wherein the plurality of electrodes areconfigured to couple to a defibrillator, and wherein the processor, thememory, and the output device are disposed in the defibrillator.
 12. Theapparatus of claim 1, wherein the one or more chest compression sensorscomprise an accelerometer assembly configured to move with a patient'schest and a caregiver's hands.
 13. The apparatus of claim 12, whereinthe signals representative of chest displacement comprise accelerationsignals.
 14. The apparatus of claim 13, wherein the processor isconfigured to doubly integrate the acceleration signals and determine achest displacement from the doubly integrated acceleration signals. 15.The apparatus of claim 1, wherein the airflow activities comprisepatient respiration or patient ventilation.
 16. The apparatus of claim1, wherein the feedback comprises one or more of visible feedback andaudible feedback.
 17. The apparatus of claim 1, wherein the feedback foradjusting the ventilations of the patient includes cardiopulmonaryresuscitation instructions.
 18. The apparatus of claim 1, wherein thesignals representative of the airflow activities of the patient indicateover ventilation of the patient.
 19. The apparatus of claim 18, whereinthe feedback for adjusting the ventilations comprises an instruction toreduce a ventilation frequency.